1. Field of the Invention
The present invention generally relates to methods for mounting electronic components. More specifically, the present invention relates to a method for mounting plural electronic components on a supporting board via adhesives.
2. Description of the Related Art
As one method for mounting electronic components such as semiconductor elements on a supporting board such as a wiring board, there is a method for providing, in advance, a paste adhesive to mounting parts for the electronic components of the supporting board and then pressing the electronic components suctioned and held by a suction tool to the mounting parts where the adhesives are provided so as to fix the electronic components on the supporting board.
Such a method is applied when plural semiconductor elements are mounted on a large size supporting board by using a so-called flip-chip bonding (face-down bonding) method or a so-called die bonding method.
In this method, there is a step for providing the adhesives on electronic component mounting expected parts of the wiring board and a step for mounting the electronic components on the electronic component mounting expected parts separately from each other. In addition, since processes for providing the adhesives are continuously implemented in the step for providing and processes for mounting the electronic components are continuously implemented in the step for mounting, it is possible to improve productivities.
In this method, providing and forming of the adhesives on the electronic component mounting expected parts of the wiring board are implemented by a dispensing method, a printing method or a transferring method.
In the dispensing method, it is possible to easily form minute adhesive patterns. The adhesives can be provided and formed with high precision and various kinds of patterns by using a robot dispenser.
In addition, a circular-shaped pattern situated in a center part of the electronic component mounting expected part, a substantially rectangular-shaped pattern having a configuration similar to a fixed area of the electronic component, a multipoint pattern, a radial pattern where plural lines cross each other in a center part, or the like is applied as a pattern configuration of the adhesive formed on the supporting board. See, for example, Japanese Laid-Open Patent Application Publication No. 11-176849.
A pattern for providing and forming the adhesive is properly selected based on the size of the electronic component to be mounted on the supporting board, material physical properties of the adhesive, the material of the surface of the supporting board, operating condition at the time of mounting such as the load, temperature, and others.
A fixing surface of the electronic component such as a semiconductor element normally has a substantially rectangular-shaped configuration. Accordingly, volume distribution of the adhesive can be made equally by forming the configuration of the providing or forming pattern of the adhesive on the electronic component mounting expected part of the supporting board with a point symmetrical shape. As a result of this, when the electronic component is pressed onto the adhesive by using a suction tool so as to be fixed on the supporting board, the adhesive can be equally spread in a substantially point symmetrical shape from the center part of the electronic component mounting expected part of the supporting board. As a result of this, the fixing surface of the electronic component comes in even contact with the adhesive so as to be fixed on the supporting board.
FIG. 1 is a first cross-sectional view showing a related art method for mounting semiconductor elements on a wiring board. In an example shown in FIG. 1, a semiconductor device is mounted on the supporting board by using a so-called flip-chip bonding (face-down bonding) method.
Paste adhesives 2 are provided on plural semiconductor element mounting expected parts S provided on an upper surface of a supporting board 1. Electrode terminals 3 are provided at each semiconductor element mounting expected part S. The electrode terminals 3 correspond to outside connection terminals of the semiconductor elements to be mounted.
On the other hand, a main surface of a semiconductor element 4 where outside connection terminals 5 are provided is made to face the supporting board 1 and the semiconductor element 4 is suctioned and held by the suction tool 6. In addition, the outside connection terminals 5 of the semiconductor element 4 and the electrode terminals 3 of the supporting board 1 are made to face each other so that positioning is made. See FIG. 1(a).
At this time, inside the suctioning part 7 of the suction tool 6 is a negative pressure. The negative pressure is maintained until suctioning of the semiconductor element 4 by the suction tool 5 is turned off.
Next, the suction tool 6 is lowered so that the semiconductor element 4 is fixed on the supporting board 1 via the adhesive 2 and the outside connection terminals 5 of the semiconductor element 4 and the electrode terminals 3 of the supporting board 1 are connected to each other. See FIG. 1(b).
After that, the suctioning of the semiconductor element 4 by the suction tool 6 is turned off and the suction tool 6 is raised. See FIG. 1(c).
At this time, in order to securely turn off the suctioning of the semiconductor element 4 by the suction tool 6, the inside of the suctioning part 7 of the suction tool 6 that has the negative pressure is switched to a positive pressure so that compressed air W is jetted from the suctioning part 7 to the circumference. See the arrows in FIG. 1(c).
Thus, according to the related art method shown in FIG. 1, when the semiconductor elements 4 are continuously mounted and fixed on plural semiconductor element mounting expected parts S of the supporting board 1, after the semiconductor element 4 suctioned and held by the suction tool 6 is fixed on the semiconductor element mounting expected part S, suctioning by the suction tool 6 is stopped and the suction tool 6 is raised while the compressed air is jetted from the suction tool 6 to the circumference.
FIG. 2 is a second cross-sectional view showing the related art method for mounting the semiconductor elements on the wiring board. In FIG. 2, parts that are the same as the parts shown in FIG. 1 are given the same reference numerals, and explanation thereof is omitted.
The paste adhesives 2 are provided on the plural semiconductor element mounting expected parts S provided on the upper surface of the supporting board 1. The electrode terminals 3 are provided at each semiconductor element mounting expected part S. The electrode terminals 3 correspond to outside connection terminals of the semiconductor element to be mounted.
On the other hand, the main surface of the semiconductor element 4 where the outside connection terminals 5 are provided is made to face the supporting board 1 and the semiconductor element 4 is suctioned and held by a suction tool 7. Hole forming parts 9 are provided in the circumference of the suctioning part 8 of the suction tool 7 configured to take suction on the semiconductor element 4. See FIG. 2(a).
While the compressed air W is jetted from the hole forming parts 9 of the suction tool 7, the suction tool 7 is lowered so that the semiconductor element 4 is fixed on the supporting board 1 via the adhesive 2 and the outside connection terminals 5 of the semiconductor element 4 and the electrode terminals 3 of the supporting board 1 are connected to each other. See FIG. 2(b).
At this time, since the compressed air W is jetted from the hole forming parts 9 of the suction tool 7 to the circumference, the adhesive 2 is made to spread and flow to the circumference of the semiconductor element 4. As a result of this, it is possible to prevent the adhesive 2 from creeping up along side surfaces of the semiconductor element 4 so that adhesion of the adhesive 2 to the suction tool 6 can be prevented.
After that, the suctioning of the semiconductor element 4 by the suction tool 7 is turned off and the suction tool 7 is raised. See FIG. 2(c). At this time, jetting of the compressed air W from the hole forming parts 9 of the suction tool 7 is stopped.
In the related art shown in FIG. 1, at the time when the suctioning of the semiconductor element 4 by the suction tool 6 is turned off, the compressed air W is jetted from the suctioning part 7 of the suction tool 6 to the circumference. On the other hand, in the related art shown in FIG. 2, while the compressed air W is jetted from the hole forming parts 9 of the suction tool 7 to the circumference, the suction tool 7 is lowered.
Because of this, as shown in parts surrounded by dotted lines in FIG. 1(c) and FIG. 2(c), due to the jetted compressed air W, the configuration pattern of the adhesive provided on a surface of a neighboring or adjacent semiconductor element mounting expected part S where the semiconductor element is not yet mounted may be deformed. In other words, an offset may be formed in the volume distribution of the adhesive 2 at the semiconductor element mounting expected part S.
As a result of this, when the semiconductor element 4 is mounted on the semiconductor element mounting expected part S, the adhesive 2 on the semiconductor element mounting expected part S cannot be equally spread.
Because of this, at a part where the volume distribution of the adhesive 2 is small, a void or non-filling part is generated. This may cause the semiconductor element 4 to be inclined and fixed when the adhesive 2 is cured after the semiconductor element 4 is mounted.
On the other hand, at a part where the volume distribution of the adhesive 2 is large, when the semiconductor element 4 is fixed, the adhesive 2 is spread and flows to the circumference of the semiconductor element 4. As a result of this, the adhesive 2 which flows out creeps up along the side surfaces of the semiconductor element 4 so as to be adhered to the suction tool.